We respond to calls for more research to address whether and how successful professional development (PD) experiences (defined here in terms of student progress) are related to changes in teacher beliefs, specifically about effective literacy instruction for young struggling readers. We developed a measure, a Teacher Belief Score, to identify teacher beliefs present in interview data and we used student achievement data to create two contrasting groups of teachers, those whose students had lower progress and those who had higher. While initially in the fall, lower progress and higher progress teachers differed little in their alignment of beliefs with program features; over time, higher progress teachers trended toward beliefs that were aligned with program features, whereas lower progress teachers trended away. Findings suggest the need for an additional component to Guskey's model of teacher change: attributing student progress to the new instructional practices learned in PD.